Propulsion system



Nov. 24, 1964 R. D. scHuL'rz PRoPuLsIoN SYSTEM Filed octA 19, 1961 DJM-Im @N wm INVENTOR. ROBERT D. SCHULTZ ATTORNEY United States Patent@ hio r Filed Oct. 19, 1961, Ser. No. 146,099 12 Claims. (Cl. 60-35.3)

This invention generally relates to a thrust propulsion system suitable forfuse in outer space, and to an improved engine employing charged droplets of colloidal size inparticular. v-

Prior development in the field of space propulsion has shown that-devices-ejecting jets of highly charged colloidal-sized droplets. are an ideal means of'thrust generation. As used hereinafter, a colloid shall be understood to mean a substance-in a state of .fine division wherein itsV constituent particles range in diameter from about 0.2 to about 0.005 micron. Such a charged colloid propulsion system is described in Patent application Serial No. 71,329, led- November 23, 196() by Robert D. Schultz, Lane K.Branson, and Robert F. Chaiken, entitled Propulsion Means, and .assigned to the assignee of the present inventionfnowPatent No. 3,122,882. In the system described therein, the invention comprises a unique propulsion unit operable within a substantial vacuum wherein colloidal-sized electrically charged liquid particles or droplets are ejected from a point or points in contiguity with the liquid container. The charged particles are focusedand accelerated through a gradient elec-iu trostatic field to produce thrust in a given direction. The ejection of colloid particles causes thrust, in accordance With the principles of classical physics, that is, for every action, there is an equal and opposite reaction. In the present device, this action reaction phenomena occurs as magnetic field interaction between the field of the colloid particles and of the accelerating rings. As the accelerating fieldpushes the colloid particles outone end of the chamber, the field of the colloid'particles creates an equal and opposite reaction against the accelerating rings, thus pushing the chamber forward. ForV optimum operation of such a system liquidsselected as besttforming colloidal-sized particles under the conditions described have been those having a vapor pressure of -5 Hg or lower at centigrade and electrical conductivity greater thany 6x10-8 milo/centimeter but less than l0-5 mho/ centimeter. Other desirable characteristics for the propulsion iiuid are: An internal pressure greater than 7 l09 dynes per sq. centimeter; a dielectric constant greater than 6; a density of about l to 11/2 grams/ centimeter 3; and a freezing point as low as possible, consistent with the above properties.

While the system described in this prior application provides satisfactory operation, it has been found that higher eiciency is obtained when volatile constituents are removed from the liquid, thereby eliminating corona discharge during operation. The presence of corona discharge may produce undesirable, extraneous ions in the colloid bea-m, the net effect of which is to waste the power of the propulsion vsystem while contributing relatively little to the thrust. However, purification which may reduce the vapor pressure of the material to 5 10r6 mm. Hg or lower, while eliminating the presence of corona discharge, will also detrimentally effect the mechanism by which the electrical atomization takes placeand derogates the generation of thrust. The underlying reason for `the above-mentioned phenomenon has not been deiinitely established. Such evidence as is available, however, substantiates the explanation set forth below.

In the embodiments described in application Serial No. 71,329 an appreciable corona discharge will occur in the vicinity of the sharp ejection points of the spray bank ICC assembly at a positive potential as low as 20 kilovolts in the .presence of air. The positive ions formed` in the corona discharge are repelled from the .positive charge tip or spray bank ejection point. The negative electrons, however, are accelerated toward the tip where they collide with the fiuid particles with sufficient energy to ionize them.

This process may be described in equation form as:

where RH represents an oil molecule, (e)* represents an `energetic electron whichhas been accelerated in the anode fallVI region of the` corona surrounding the needle point, ecis -an electron after collision which is free to migrate in the oil filmuat the tip, and RH+ represents a singly ionized oil molecule. It is possible to vestablish a field` intensity at the lejection point or tip of the same magnitude as the apparent electric strength of organic liquids. As corroborated inan article describing electrical breakdown mechanism `by T.l I. Lewis in 27 Journal of Applied Physics, page 645 (1956), the` electrons e; condensed in the surface of the oil are capable, at field inf tensities easily generated by the propulsion systeml described, of rapidlymigrating through the oil to the metal of the ejection point, where they disappear into the conduction band. l This permits the heavy ions RH+ to ac cumulate in the external surface of the oil. covering the needle point ,until their mutual electrostatic repulsion (i.e., the `electrostatic pressure) rises to a value sufiicient to overcome the tensile strength of the oil. By tensile strength of the Loil is meant intermolecular cohesion between the molecules at or below the surface of the oil film. fThe oil then ruptures into fairly uniform-sized colloidal droplets whose surfaces contain an appreciable number `of RH+ ions. ,When the ambient gas pressure is reduced to avalue of 5 X10*6 mrn. Hgor less, the mean free-paths of electrons and positive ions moving in the residual gas become large compared to the gap between electrodes.` Under these high vacuum conditions, a selfsustained corona discharge is impossible, a negligible quantity of energetic (e-)i electrons are available to ionize the oil molecules into RH+ ions, and the electrical atornizationV process is attenuated.

Thus, in order to obtain charged liquid colloids by electrical atomization under the vacuum conditions of outer space, it will be necessary to provide charge. carriers, that is, substitutes for either the (erf: electrons of the corona discharge or for the RH?t particles which are produced in Vthe liquid surface. As used herein, the term charge carrier is understood to mean a substance which will supply electrons capable of being Vaccelerated from a posi-tively charged ejection means, or which will supply positively charged particles capable of being accelerated from a negatively charged eject-ion means. c

It is therefore the principa-l object of the present invention to provide a novel method of and improved means for charged colloid propulsion of a space flight vehicle. Another object of the` present invention Iis to provide a novel method vof and `improved means for improving the efliciencyof avr charged colloid propulsion system.

In its principal aspect,the present invention comprises a unique propulsion unit operable within .an atmosphere of substantial vacuum whereincolloidal sized electrically chargedl particles or droplets of purified liquid are4 ejected froma spray bank.v Means are provided for supplying charge carriers to the iiuid to permit automatic charging at the particle ejection points. The charged particles are then focused and accelerated through a gradient electro? static field. to produce thrust in a given direction. Means associated with said focusing and accelerating means may be provided, for neutralizingthe effect of space charge on said beam of particles.

These and other objects, aspects, and features of this invention Will be apparent to those skilled in the art from the following more detailed description taken together with the appended drawing, which is a schematic view of the improved propulsion system of the present invention.

As shown in the drawing, the propulsion unit comprises a spray bank 26 and associated apparatus. The spray bank 26 comprises a chamber or container 32 in which the propulsive liquid 34 is confined. This liquid is subjected to a high positivee voltage by means of a circular electrode 36 which encompasses the container 32 and is connected to the first or positive power lead 2t). Openings 28 on one phase of the confining chamber 32 are provided through which the liquid migrates under the inuence of a force such as applied pressure or capillary attraction. The spray bank assembly 26 illustrated here comprises a first plate t) to which are attached steel pins 52 of a small diameter, for example, approximately .030. The pins protrude through a similar pattern of holes 2S which have a diameter of approximately .003 greater than `the diameter of the pins, the holes being in a second plate 54. Between the two plates 50, 54 is provided a reservoir for the fluid 34 to be dispensed. The rounded configuration of the high voltage electrode 36 is provided to prevent high voltage leakage from the shap corners of the plates S0, 54. A high positive voltage (for positively charged colloids), shown here, or a high negative voltage (for negatively charged colloids) may be applied to the high voltage electrode 36. The high voltage is transmitted to the points of the pins 52 and a spray 40 of charged particles is produced. The fluid 34 flows from the reservoir down the pins 52, maintaining the spray 40. This flow is produced .by gravity and capillary action, but could be produced by pressurizing the fluid 34 in the reservoir, in the absence of a high gravitational field. A pair of spacers 56 are provided between the plates 50, 54 to provide the proper chamber rigidity. Other types of spray banks and associated components may be used by the propulsion unit of this invention. Possible variations of the spray bank are fully disclosed in the previously mentioned copending patent application Serial No. 71,329 titled Propulsion Means by Robert D. Schultz, Lane K. Branson, and Robert F. Chaiken, assigned to the assignee of the present invention, now Patent No. 3,122,882.

A drift tube assembly 38 is arranged adjacent the discharge openings 28 of the confined chamber 34. The assembly 38 comprises drift tubes or accelerating rings spaced in a manner surrounding the proposed path of the charged colloidal droplets 40. The drift tube 42 furthest in distance from the spray bank 26 is connected to the negative power lead of an external power supply, not shown. The drift tube 30 closest to the spray bank 26 is connected to the positive power lead of the external power supply through a portion 44 of the voltage divider 46. It is seen that the potential gradient between the iiuid 34 and the spray bank assembly 26 and the furthest drift tube 42 is provided by the presence of the voltage divider 46, the individual drift tubes achieving their potential from voltage taps intermediate the length of the voltage divider 46. By this means, an electrostatic field is provided which has a potential gradient varying from a maximum (positive) value at the spray bank 26, ground or neutral at the first drift tube 30, to a high (negative) value at the furthest drift tube 42. It is to be understood that it is fully within the scope of this invention to employ a grid arrangement rather than drift tubes, or even to employ electromagnetic focusing and acceleration.

The means employed to provide substitutes for either the (e)* electrons for the corona discharge or for the RH+ ions are shown in this ligure as an electron source 100 in juxtaposition to the ejection points of the spray bank which are covered with the liquid to .be atomized. The electron source 100 may be, for example, a hot lilament or a cold-cathode emitter. A bias of up to several hundred volts or more is necessary to accelerate the electrons from the source to the dispersing tips or knife edges -in order to ionize the fluid molecules. The rate of formation of RH+ ions can be controlled by adjusting the bias voltage, by adjusting the heater current to an indirectly heated cathode, or by varying the exposed area of the electron emitter. In the embodiment shown, a variable resistance 102 is utilized to vary the bias, although the other means described could be used to accelerate the electrons from the electron source 100.

It is believed that the rate of formation of RH+ ions will inliuence the size of the resulting charged liquid colloidal particles and their vcharge-to-mass ratio. It follows that it is possible to produce positively charged liquid colloid particles in a vacuum with a charge-to-mass ratio as high as 109 to 1010 e.s.u./g. Such charge-tomass ratios enable reduction of the accelerating voltage required `to attain a given speciiic impulse, and enables generation of thrust comparable to that produced by ion propulsion systems.

In the embodiment shown, a shield member 45 within which is located an electron or negative ion emitter 48 is located adjacent the rearmost accelerating drift tube or ring 42. The shield 45' is connected to be at the same high negative potential as the furthest drift tube or ring 42, and the emitter 48 is powered by a separate voltage source, not shown. It is the function of the emitter 48 to inject negative particles into the beam 40 of colloidal droplets to overcome the space-charge repulsion phenomenon, while the shield 45 insures that the negative par- -ticles are confined to the vicinity of the beam 40. The

emitter 48 may, by way of example, comprise an indirectly heated cathode powered by the previously mentioned separate voltage source, or merely a hot filament, similarly powered. Other space charge neutralization means such as, for example, a rarefied neutral gas stream, may be utilized.

In operation, the purified liquid 34 having the abovedescribed characteristics, is directed to the extremities of the dispersion means associated with the fluid reservoir 32. Several examples of fluids suitable for use in such a system are dioctylphthalate, polypropyleneglycol, or glycerine. Colloidal sized electrically charged particles are ejected from the spray bank 25 which is at the same high potential as the iiuid reservoir. Negative charge carriers are provided to the colloid stream by the electron source 100, and the stream of particles is then focused and accelerated through a gradient electrostatic field and directed to the ambient to produce thrust in accordance with the principles of classical physics.

. While the operation of a system, as explained above, is believed to be a correct explanation of the principles underlying my invention, further investigation may lead to a modification of my theory. It is to be understood, however, that the invention is independent of any theory which may be advanced to account for the results obtained. In explaining my invention, I have illustrated and described many details of construction, but it is obvious that alternatives and equivalents will occur to those skilled in the art which are within ythe scope and spirit of my invention. It is my desire, however, that my protection not be limited to the details herein illustrated and described, but only by the proper scope of the appended claims:

I claim:

1. A method of creating thrust in a vacuum atmosphere comprising the steps of applying an electrical potential to a body of purified liquid having a vapor pressure not greater than 105 mm. Mg about 20 centigrade and an electrical conductivity greater than 6X 10-8 mho/centimeter ybut less than 10-5 mbo/centimeter, which is confined in a means having a minute openings; directing said charged liquid to the extremities of dispersion means associated with said openings, whereby charged liquid particles of colloidal size will be formed at said dispersion means extremities; directing negatively charged particles from an external source to said colloidal particles; ejecting said particles from said dispersion means in a beam; `focusing and accelerating said beam particles; and neutralizing the effect of space charge on said lbeam `of particles.

2. A propulsion system operable in a vacuum atmosphere comprising: a reservoir having a plurality of openings on the surface thereof; a body of fluid having a vapor pressure not greater than .l0-5 mm. Hg at about 20 centigrade and an electrical conductivity greater than 6 l08 mbo/centimeter but less than l0-5mho/centimeter arranged in said reservoir; fluid ejection means associated with said openings in said surface; means for applying electrical potential to said fluid body and said reservoir; negative particle emission means arranged in contiguity to said fluid ejection means; and electric focusing and accelerating ine-ans arranged in contiguity to said negative particle emission means.

3. A propulsion system as described in claim 2, and, in addi-tion, means for space charge neutralization, said neutralization means being associated with said focusing and acceleration means.

4. A reaction propulsion system for producing thrust in a substantial vacuum comprising: a body for purified liquid having a vapor pressure not greater than -5 mm. Hg at about 20 centigrade and an electrical conductivity greater than 6x10-8 mho/centimeter but less than 10-5 mho/ centimeter; means for confining said body of liquid, said confining means having minute openings through which liquid may migrate; liquid dispersion means in contiguity with said minute openings; means for subjecting said confined liquid to a relatively high electric potential; a negative particle emission source arranged in contiguity to said liquid dispersion means; means Vfor creating and maintaing a gradient electric field in lspaced relationship to said dispersion means, whereby charged colloidal-sized droplets of the liquid are ejected from said dispersion means as the result of said high potential, and are focused and accelerated in any f desired direction; and means for injecting negative particles into said droplets after they have been focused and accelerated.

5. The reaction propulsion system of claim 4 wherein said liquid is selected from the group consisting of dioctylphthalate, polypropyleneglycol, and glycerine.

6. A reaction propulsion system as described in claim 4 wherein said negative particle emission source comprises a cold cathode emitter.

7. A reaction propulsion system as described in claim 4 wherein said negative particle emission source comprises a hot filament.

8. A system for creating thrust in a vacuum atmosphere comprising: a reservoir having a plurality of openings on one surface thereof; a body of liquid having a vapor pressure not greater than 10-5 mm. Hg at about centigrade and an electrical conductivity greater than 6x10-8 mho/centimeter but less than 10-5 mho-centimeter arranged in said reservoir; fluid ejection means associated with said openings in said surface; negative particle emission means externally associated with said uid ejection means; electrostatic focusing and accelerating means arranged in contiguity to said fluid ejection means; means for applying electric potential to said liquid body through said reservoir and said electrostatic focusing and accelerating means, a difference of potential existing between said reservoir and said electrostatic focusing and accelerating means whereby liquid particles of colloid size are ejected from said particle ejection means in a beam and said beam is focused and accelerated by said electrostatic focusing and accelerating means; and means associated with said electrostatic focusing and accelerating means for neutralizing the effect of space charge on said beam of particles.

9. A propulsion system operable in a vacuum atmosphere comprising: a reservoir having a plurality of openings in one surface thereof; a body of liquid in said reservoir, said liquid having a vapor pressure not greater than 10-5 mm. Hg at about 20 centigrade, an internal pressure greater than about 7 109 dynes per square centimeter, an electric conductivity substantially between 6x10"8 andlO*5 mbo/centimeter, a dielectric constant greater than 6, and a density substantially between 1 and 11/2 grams/ cm; fluid ejection means associated with said openings in said surface; negative particle ejection means externally associated with said uid ejection means; electrostatic focusing and accelerating means in spaced relation with said iluid ejection means; means for applying electric potential to said liquid body, said reservoir and said focusing and laccelerating means, 'whereby the liquid body and reservoir are at a potential of approximately l0() kilovolts of one polarity and a gradient electric field is crea-ted which Varies from zero in the vicinity of said ejection means to approximately 1000 kilovolts of an opposite polarity at the position of said focusing and accelerating means furthest extended from said iiuid ejection means; and means associated with said focusing and accelerating means for neutralizing the effect of space charge, said neutralization means being juxtaposed with said focusing land accelerating means which is at a potential of approximately 1000 kilovolts.

l0. A reaction propulsion system as described in claim 4 wherein said negative particle emission source comprises an indirectly heated cathode.

1l. A propulsion system operable in a vacuum atmosphere comprising: means for ejecting ya colloidal stream of electrically charged atomized liquid droplets of colloidal dimensions, means for injecting negatively charged particles into said colloidal stream, and electric focusing and acceleration means arranged in contiguity to said colloidal particle ejection meansv and said negatively charged particle injection means whereby liquid particles of colloidal dimensions are ejected in a stream and said stream is focused and accelerated by said electric focusing and accelerating means.

12. A system as described in claim 11, and in addition, means for neutralizing the effect of space charge on said colloidal-sized fluid particle stream by injecting negative particles into said colloidal sized fluid particle stream after it has been focused and accelerated, said neutralizing means being associated with said electric focusing and acceleration means.

References Cited in the tile of this patent UNITED STATES PATENTS Cook Nov. 17, 1942 

1. A METHOD OF CREATING THRUST IN VACUUM ATMOSPHERE COMPRISING THE STEPS OF APLYING AN ELECTRICAL POTENTIAL TO A BODY OF PURIFIED LIQUID HAVING A VAPOR PRESSURE NOT GREATER THAN 10**-5 MM. MG ABOUT 20* CENTIGRADE AND AN ELECTRICAL CONDUCTIVITY GREATER THAN 6X10**-8 MHO/CENTIMETER BUT LESS THAN 10**-5 MHO/CENTIMETER, WHICH IS CONFINED IN A MEANS HAVING A MINUTE OPENINGS; DIRECTING SAID CHARGED LIQUID TO THE EXTREMITIES OF DISPERSION MEANS ASSOCIATED WITH SAIS OPENINGS, WHEREBY CHARGED LIQUID PARTICLES OF COLLODIDAL SIZE WILL BE FORMED AT SAID DISPERSION MEANS EXTREMITIES; DIRECTING NEGATIVELY CHARGED PARTICLES FROM AN EXTERNAL SOURCE TO SAID COLLOIDAL PARTICLES; EJECTING SAID PARTICLES FROM SAID DISPERSION MEANS IN A BEAM; FOCUSING AND ACCELERATING SAID BEAM PARTICLES; AND NEUTRALIZING THE EFFECT OF SPACE CHARGE ON SAID BEAM OF PARTICLES. 